Dialysis systems and methods including cassette with fluid heating and air removal

ABSTRACT

A dialysis fluid system includes an instrument including a pump actuator and a fluid heater, and a dialysis fluid cassette. The dialysis fluid cassette includes a rigid portion defining a pumping section for operation with the pump actuator and a heating section for operation with the fluid heater. The heating section includes a dialysis fluid inlet, a dialysis fluid outlet, and a dialysis fluid heating area located between the fluid inlet and the fluid outlet, the heating section further includes an air separation chamber for collecting air separated from the dialysis fluid.

PRIORITY

This application claims priority to and the benefit as a divisionalapplication of U.S. patent application entitled, “Dialysis SystemsHaving Air Separation Chambers With Internal Structures To Enhance AirRemoval”, Ser. No. 11/865,583, filed Oct. 1, 2007, the entire contentsof which are incorporated herein by reference and relied upon.

BACKGROUND

The examples discussed below relate generally to medical fluid delivery.More particularly, the examples disclose systems, methods andapparatuses for dialysis such as hemodialysis (“HD”) automatedperitoneal dialysis (“APD”).

Due to various causes, a person's renal system can fail. Renal failureproduces several physiological derangements. It is no longer possible tobalance water and minerals or to excrete daily metabolic load. Toxic endproducts of nitrogen metabolism (urea, creatinine, uric acid, andothers) can accumulate in blood and tissue.

Kidney failure and reduced kidney function have been treated withdialysis. Dialysis removes waste, toxins and excess water from the bodythat normal functioning kidneys would otherwise remove. Dialysistreatment for replacement of kidney functions is critical to many peoplebecause the treatment is life saving.

One type of kidney failure therapy is Hemodialysis (“HD”), which ingeneral uses diffusion to remove waste products from a patient's blood.A diffusive gradient occurs across the semi-permeable dialyzer betweenthe blood and an electrolyte solution called dialysate to causediffusion. Hemofiltration (“HF”) is an alternative renal replacementtherapy that relies on a convective transport of toxins from thepatient's blood. This therapy is accomplished by adding substitution orreplacement fluid to the extracorporeal circuit during treatment(typically ten to ninety liters of such fluid). That substitution fluidand the fluid accumulated by the patient in between treatments isultrafiltered over the course of the HF treatment, providing aconvective transport mechanism that is particularly beneficial inremoving middle and large molecules (in hemodialysis there is a smallamount of waste removed along with the fluid gained between dialysissessions, however, the solute drag from the removal of thatultrafiltrate is not enough to provide convective clearance).

Hemodiafiltration (“HDF”) is a treatment modality that combinesconvective and diffusive clearances. HDF uses dialysate flowing througha dialyzer, similar to standard hemodialysis, to provide diffusiveclearance. In addition, substitution solution is provided directly tothe extracorporeal circuit, providing convective clearance.

Most HD (HF, HDF) treatments occur in centers. A trend towards homehemodialysis (“HHD”) exists today in part because HHD can be performeddaily, offering therapeutic benefits over in-center hemodialysistreatments, which occur typically bi- or tri-weekly. Studies have shownthat a patient receiving more frequent treatments removes more toxinsand waste products than a patient receiving less frequent but perhapslonger treatments. A patient receiving more frequent treatments does notexperience as much of a down cycle as does an in-center patient who hasbuilt-up two or three days worth of toxins prior to a treatment. Incertain areas, the closest dialysis center can be many miles from thepatient's home causing door-to-door treatment time to consume a largeportion of the day. HHD can take place overnight or during the day whilethe patient relaxes, works or is otherwise productive.

Another type of kidney failure therapy is peritoneal dialysis, whichinfuses a dialysis solution, also called dialysate, into a patient'speritoneal cavity via a catheter. The dialysate contacts the peritonealmembrane of the peritoneal cavity. Waste, toxins and excess water passfrom the patient's bloodstream, through the peritoneal membrane and intothe dialysate due to diffusion and osmosis, i.e., an osmotic gradientoccurs across the membrane. Osmotic agent in dialysis provides theosmotic gradient. The spent dialysate is drained from the patient,removing waste, toxins and excess water from the patient. This cycle isrepeated.

There are various types of peritoneal dialysis therapies, includingcontinuous ambulatory peritoneal dialysis (“CAPD”), automated peritonealdialysis (“APD”), tidal flow dialysate and continuous flow peritonealdialysis (“CFPD”). CAPD is a manual dialysis treatment. Here, thepatient manually connects an implanted catheter to a drain to allowspent dialysate fluid to drain from the peritoneal cavity. The patientthen connects the catheter to a bag of fresh dialysate to infuse freshdialysate through the catheter and into the patient. The patientdisconnects the catheter from the fresh dialysate bag and allows thedialysate to dwell within the peritoneal cavity, wherein the transfer ofwaste, toxins and excess water takes place. After a dwell period, thepatient repeats the manual dialysis procedure, for example, four timesper day, each treatment lasting about an hour. Manual peritonealdialysis requires a significant amount of time and effort from thepatient, leaving ample room for improvement.

Automated peritoneal dialysis (“APD”) is similar to CAPD in that thedialysis treatment includes drain, fill and dwell cycles. APD machines,however, perform the cycles automatically, typically while the patientsleeps. APD machines free patients from having to manually perform thetreatment cycles and from having to transport supplies during the day.APD machines connect fluidly to an implanted catheter, to a source orbag of fresh dialysate and to a fluid drain. APD machines pump freshdialysate from a dialysate source, through the catheter and into thepatient's peritoneal cavity. APD machines also allow for the dialysateto dwell within the cavity and for the transfer of waste, toxins andexcess water to take place. The source can include multiple steriledialysate solution bags.

APD machines pump spent dialysate from the peritoneal cavity, though thecatheter, and to the drain. As with the manual process, several drain,fill and dwell cycles occur during dialysis. A “last fill” occurs at theend of APD and remains in the peritoneal cavity of the patient until thenext treatment.

In any of the above modalities, entrained air and other gases are aconcern. Entrained air can cause inaccuracies when pumping dialysate foreither PD or HD. Entrained air can cause a reduction in effectivesurface area in a hemodialysis filter when it accumulates on the filterfibers, leading to a reduction in effectiveness of the therapy.Entrained air entering a patient's peritoneum during PD can causediscomfort. Entrained air entering a patient's bloodstream during HD canhave severe consequences. Accordingly, a need exists to provide anapparatus that ensures that entrained air is removed from dialysate orblood prior to delivering such fluids to the patient.

SUMMARY

The present disclosure relates to air and gas removal for dialysissystems and extracorporeal devices, e.g., blood separation, bloodwarming, etc. The structures disclosed herein can be performed in anytype of peritoneal dialysis treatment or blood dialysis treatment suchas hemodialysis, hemofiltration, hemodiafiltration and continuous renalreplacement therapy. The embodiments below are disclosed in connectionwith a dialysis cassette that is loaded into a dialysis instrument. Thedialysis cassette is part of an overall dialysis set which can includeone or more supply bag, or connection to the dialysate generationsystem, one or more drain bag, a heater bag and associated tubingconnecting the bags to the dialysis cassette. The user places thedialysis cassette within the dialysis instrument for therapy. Thedialysis cassette can include one or more pump chamber, flow path and/orvalve chamber. The dialysis instrument includes one or more pumpactuator that actuates the pump chamber of the disposable cassette. Thedialysis instrument also includes one or more valve actuator thatactuates the valve chamber of the disposable cassette. The disposablecassette can also include a fluid heating pathway that operates with afluid heater of the dialysis instrument. The disposable cassette canalso include various regions for sensing pressure, fluid composition,fluid temperature, and fluid levels.

While air traps 50 are shown herein in connection with a disposable setdescribed below, the separation chambers are alternatively stand-aloneapparatuses that operate independent of the disposable cassette.Further, the present disclosure mainly discusses air but other gases canalso be present and therefore the present air separation chambers canalso trap these gases. In PD for example, gases from the patient canbecome entrained in fluid being pumped form the system. Also, gases fromdialysate concentrate, such as bicarbonate can become entrained in freshdialysate. It is expressly contemplated for the air separation chambersof the present disclosure to remove these additional types of gases.

As mentioned above, air in dialysate or dialysis fluid as well as air inblood needs to be removed before any of these fluids are eitherdelivered to a dialyzer or patient. Air can be present in the system viaair trapped in supply bags, air trapped in the tubes leading from thesupply bags to the disposable cassette, air not completely primed fromthe disposable cassette itself and air that is released from solutionwhen the dialysis fluid is mixed and/or heated. Air can also signal aleak in the disposable unit.

The air traps discussed below are shown generally in connection with adialysis fluid, such as dialysate, having entrained air. It should beappreciated however that the embodiments are applicable equally to theremoval of air from blood pumped from a patient to a hemodialyzer orhemofilter. As used herein, the term dialysis fluid includes, withoutlimitation, mixed dialysate, mixed infusate, mixed replacement fluid,concentrated components of any of these, and blood.

In one embodiment, the disposable cassette defines an air separationchamber that has a fluid inlet and a fluid outlet. An inlet valve and anoutlet valve are paired with the fluid inlet and fluid outlet of the airseparation chamber, respectively. The air separation chamber alsoincludes an air vent outlet, which is in fluid communication with one ormore air vent valve. The air removed from fluid in the air trap is sentto atmosphere, to a holding vessel such as an empty bag or a fluidfilled bag (e.g., saline bag or dialysate bag), or to a drain, forexample, whichever is desired.

In one embodiment, the air separation chamber is configured with respectto the other components of the disposable cassette such that when thecassette is loaded into the dialysis instrument, the fluid inlet andfluid outlet are located towards a bottom or bottom wall of the airseparation chamber, while the air outlet is located at or near the topof the dialysis instrument. Such configuration allows buoyancy forces tolift air bubbles from the dialysis fluid to the top of the airseparation chamber for venting.

The dialysis cassette in one embodiment includes a rigid portion, whichcan be a hard plastic. The rigid portion is formed to have pump chambers(e.g., for diaphragm pumps) or pump tubing (for peristaltic pumping),fluid pathways and valve chambers. The rigid portion also defines someor all of the air separation chamber. It is contemplated that thedisposable cassette will have flexible sheeting welded to one or bothsides of the rigid portion of the cassette. The flexible sheeting allowsa pneumatic or mechanical force to be applied to the pump chambers(e.g., diaphragm) and valve chambers to operate those chambers. It isalso contemplated that at least one outer surface of the air separationchamber consumes a portion of one or both flexible sheets. In addition,one or both sides of the dialysis cassette can be rigid.

The disposable cassette can have a base wall or mid-plane that dividesthe disposable cassette into first and second sides. For example, in oneembodiment the flow paths are provided on one side of the disposablecassette (one side of the base wall), while the pump and valve chambersare provided on the other side of the disposable cassette. In oneembodiment, the mid-plane is not present within the air separationchamber. The air separation chamber can be bonded on two sides byflexible sheeting. Alternatively, the mid-plane is not provided in theair separation chamber, however, the outer walls of the air separationchamber are rigid and adhere to the top, bottom, inlet and outlet wallsvia a suitable sealing process. Further alternatively, one outer wall isrigid, while the other outer wall is flexible sheeting.

The air separation chamber includes one or more baffle or separationwall that is configured to disrupt the flow of fluid through the airseparation chamber, promoting the separation of air from the dialysisfluid. In one embodiment, the baffle or separation wall extendshorizontally to separate a dialysis fluid inlet from a dialysis fluidoutlet. The inlet and outlet here are formed in an internal side wallformed by the rigid portion of the cassette. The inlet and outlet can beformed in the same internal side wall or in different internal sidewalls. The inlet can be provided below the outlet or vice versa. Theinlet and outlet are alternatively vertically disposed with respect tothe air separation chamber. In one embodiment, the baffle or separationwall extends from one internal side wall to the other internal sidewall, forcing the dialysis fluid over the free or distal end of thebaffle.

The baffle or separation wall extends vertically up the air separationchamber, ending at a free end at which the dialysis fluid flows over anddown towards the dialysis fluid outlet located on the opposite side ofthe baffle or separation wall. The baffle accordingly forces thedialysis fluid to make an inverted-U-like flow path.

The inlet or “filling” side of the baffle or separation wall in oneembodiment is angled or tapered inwardly towards a center of the airseparation chamber. This feature serves a number of purposes. First, theangle or taper causes the cross-sectional area of the dialysis fluidflow to increase as it rises up the inlet side of the baffle so that thefluid flow velocity decreases. The slowing of the dialysis fluidvelocity also reduces the velocity of the air bubbles that are travelingwith the fluid. When the fluid flow direction changes from verticallyupward to horizontal and then vertically downward, as it is directedtowards the exit on the opposite side of the separation wall, thebuoyancy forces are able to overcome the drag exerted on the air bubblesby the increasingly slower moving fluid flow. The air bubbles can thenfloat into the collection portion at the top of the air trap.

Second, the horizontal flow section at the top of the vertical wall hasno downward velocity component so the air bubbles are momentarily freeto float up into the air collection portion at the top of the air trap.As the fluid direction changes from horizontal to vertically down, theair bubbles continue to be separated from the flow of the dialysissolution as it turns downward and flows toward the outlet. Thevertically oriented air separation wall can have multiple tapers orbends as desired. It can also have flow directors that spread the flowuniformly along the vertically oriented separation wall.

In one embodiment, the horizontal flow section at the top of verticalwall is lengthened by a horizontally disposed baffle, or separationwall. This further enhances the air separation since the air bubbles arenot acted upon by a downward drag force for a longer period of time. Thehorizontal section can slope slightly upward so that the air bubbleshave both a buoyancy force and a velocity force to counter the dragproduced by the fluid when it begins to flow vertically downward.

The second separation wall can be provided alternatively fluidly aheador upstream of the first, e.g., tapered, baffle to provide a series orcombination of dialysis fluid direction changes, for example, to providea serpentine flow path. Here, the inlet and outlet can be disposedvertically with respect to the air separation chamber when mounted, toaccommodate the provision of the baffle walls in series between thedialysis fluid inlet and dialysis fluid outlet.

The dialysis fluid cassette in one embodiment includes valve chambersthat communicate fluidly with the fluid inlet, the fluid outlet and anair outlet of the air separation chamber. The valve chambers can belocated directly adjacent to the air separation chamber or furtherupstream or downstream from the air separation chamber. In onealternative embodiment, the air vent valve chamber (and port) arelocated within the air separation chamber. Here, at least one outersurface of the air separation chamber (covering the valve chamber port)is made of flexible cassette sheeting.

In one alternative embodiment, the air separation chamber includesconcentric tubes. The outer tube for example includes a dialysis fluidinlet. The inner tube extends a certain distance within the outer tubeand is a dialysis fluid outlet. Dialysis fluid entering the concentrictube air separation chamber flows vertically up along the inside of theouter tube and the outside of the inner tube before rising above theinner tube. The dialysis fluid then spills into the inner tube and flowsdownwardly out the bottom and the outlet of the tube.

The concentric tubes provide a relatively large cross-sectional area forthe dialysis fluid to slowly flow up the outside of the inner tube,allowing buoyancy forces time to dislodge the gas bubbles from thedialysis fluid. The concentric tube air separation chamber can be madepart of the disposable cassette, be connected to the disposable or beseparate from but in fluid communication with the disposable cassette.

In a further alternative embodiment, the disposable cassette provides afluid heating area that is large enough to function additionally as anair separation chamber. In certain figures illustrated below, thedisposable cassette includes a cylindrical fluid heating area. The fluidheating/air separation inlet can be located above or below the fluidheating/air separation outlet. In either case, a vent opening is locatedelevationally above both the inlet and outlet when the cassette ismounted within the dialysis instrument. This configuration isadvantageous in one respect because gas bubbles tend to come free fromthe dialysis fluid when the fluid is heated.

It is accordingly an advantage of the present disclosure to provideimproved air separation chambers for the removal of air from thedialysis fluid or from blood flowing through a disposable dialysis fluidapparatus.

Additional features and advantages are described herein, and will beapparent from, the following Detailed Description and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1 and 2 are perspective views of a disposable dialysis fluidcassette having one embodiment of a dialysis fluid air separationchamber of the present disclosure.

FIGS. 3 and 4 are perspective views showing the dialysis fluid airseparation chamber of FIGS. 1 and 2 more closely.

FIG. 5 is a sectioned elevation view of one embodiment of an airseparation chamber of the present disclosure.

FIGS. 6 to 8 show computer simulations of the operation of the airseparation chamber of FIG. 5.

FIGS. 9A and 9B are sectioned elevation and rear elevation views,respectfully, of one alternative embodiment for an air separationchamber of the present disclosure.

FIGS. 10A and 10B are sectioned elevation and rear elevation views,respectfully, of a another alternative embodiment for an air separationchamber of the present disclosure.

FIGS. 11A and 11B are sectioned elevation and rear elevation views,respectfully, of a further alternative embodiment for an air separationchamber of the present disclosure.

FIG. 12 is a perspective view of a disposable cassette and integralfluid heating/air separation chamber illustrating a further alternativeembodiment for an air separation chamber of the present disclosure.

FIG. 13 is a sectioned elevation view of a concentric tube airseparation chamber illustrating yet another alternative embodiment foran air separation chamber of the present disclosure.

DETAILED DESCRIPTION

Referring now to the drawings and in particular to FIGS. 1 and 2,dialysis cassette 10 having air trap 50 illustrates one embodiment ofthe present disclosure. As discussed herein, air trap 50 refersgenerally to each of the air traps 50 a to 50 g discussed in detailbelow. Dialysis cassette 10 is operable with any type of dialysisinstrument, such as a peritoneal dialysis instrument, hemodialysis,hemofiltration, hemodiafiltration or continuous renal replacementtherapy instrument. Dialysis cassette 10 can hold a dialysis fluid, suchas dialysate or blood. The dialysis fluid can be premixed or cassette 10can carry a component of dialysate such as a dialysate concentrate.

Dialysis cassette 10 in one embodiment is part of a disposable set,which includes one or more supply bag, a drain bag, a heater bag, andtubing running from those bags (not illustrated) to dialysis cassette10. Dialysis cassette 10 in one embodiment is disposable, however,dialysis cassette 10 could be cleaned for multiple uses in which casethe air traps described herein are used multiple times. Dialysiscassette 10 includes a rigid portion have a cassette top wall 12, acassette side wall 14 and a cassette bottom wall 16. Suitable materialsfor the rigid portion include polyvinyl chloride (“PVC”), acrylic, ABS,polycarbonate, and polyolefin blends. The rigid portion of cassette 10also includes a base wall or mid-plane 18, which separates cassette 10into first and second sides.

Cassette 10 on both sides of mid-plane 18 includes valve chambers 20 ato 20 l, which operate with a pneumatically and/or electromechanicallyoperated valve actuator located in the dialysis instrument. Certain onesof the valve chambers, namely chamber 20 k and 20 l, operate as airseparation chamber vent valve chambers. The air separation chamber may,or may not, have inlet and outlet valve chambers. The embodiment shownin FIG. 1 and FIG. 2 is intended to separate air from a flowing streamof blood and does not have either an inlet or an outlet valve chamber.Instead, pinch valves are intended to be used when it is necessary toclose off the flow in the tubing coming from the patient (arterial line)and returning to the patient (venous line). Cassette 10 also includesperistaltic pumping tubes that operate with peristaltic pump actuatorsof the dialysis instrument. The cassette can alternatively includediaphragm pump chambers that operate with a pneumatically and/orelectromechanically operated pump actuator.

Both sides of mid-plane 18 of cassette 10 include flow paths 24. Itshould be appreciated that cassette 10 can have different structurallayouts without affecting the performance of air separation chamber 50.Air separation chamber 50 can be located on either side of mid-plane 18for space purposes or for other reasons related to component layout.

In the illustrated embodiment, valve chambers 20 a to 20 l operate witha flexible cassette sheeting 28, which is welded, heat sealed or solventbonded to rigid walls 12, 14, 16, air separation chamber walls, etc., ofthe rigid portion of cassette 10. Cassette sheeting 28 is also used asthe pump diaphragm if a diaphragm pump is used instead of theperistaltic pump. Cassette sheeting 28 is also used to pump fluidthrough diaphragm when used. Suitable cassette sheeting 28 includespolyvinyl chloride (“PVC”), polypropylene/polyethylene blends,polypropylene or Kraton blends, polyester, polyolefin, and ULDPE. Thesuitable PVC sheeting can include, for example, monolayer PVC films,non-DEHP PVC monolayer films, monolayer non-PVC and multilayer non-PVCfilms (wherein different layers are chosen to provide strength,weldability, abrasion resistance and minimal “sticktion” to othermaterials such as rigid cassette materials). Multiple layers can beco-extruded or laminated with or without a gas barrier.

The dialysis instrument includes a controller unit that operates aprogram that controls when valve chambers 20 a to 20 l are open orclosed. The controller unit can include, but is not limited to, aprocessor, memory, hardware (e.g. sensors, actuators, I/O boards, etc.),software, and algorithms. For example, inlet and outlet valve chambers20 k and 20 l are open during dialysis fluid delivery and/or bloodpumping to remove air from those fluids. Inlet valve chamber 20 j isopened to delivery priming fluid directly into air separation chamber50. Inlet valve chambers 20 b and 20 c are used to deliver priming fluidinto the inlet and outlet of the peristaltic pump during priming andrinseback.

Inlet and outlet valves chambers 20 e through 20 i allow the system todirect the flow of fresh dialysate into the dialyzer secondary toperform hemodialysis or hemo-filtration, into the dialyzer primary inletto perform pre-dilution hemo-filtration or into the dialyzer primaryoutlet to perform post-dilution hemofiltration. The independent controlof the valves allows one disposable set and device to perform virtuallyany type of hemodialysis including hemo-diafiltration, CRRT, SCUF, etc.

The controller unit is also programmed to operate vent valve chambers 20k and 20 l, so as to remove air from the air separation chamber in amanner so as not to affect the sterility of the dialysis fluid flowingthrough cassette 10. To this end, the controller unit can monitor theoutputs from a single analog liquid level sensor, or multiple digitalliquid level sensors, that are maintained in contact with the flexiblefilm covering the domes shaped air collection portion of air separationchamber 50. When the liquid level sensors indicate that the liquid levelhas fallen, valve chambers 20 k is first opened so that the pressurizedair in air separation chamber 50 flows into the volume between valvechambers 20 k and 20 l. Valve 20 k is then closed trapping thepressurized air. Valve 20 l is then opened discharging the pressurizedair. The controller unit is programmed to repeat the valve sequence forvalve chambers 20 k and 20 l as required in order to maintain thedesired liquid level in air separation chamber 50.

Cassette 10 in FIG. 1 also includes a plurality of rigid ports 26 a to26 f extending from one of the walls, such as cassette top wall 12.Rigid port 26 c draws the blood from the patient (arterial line) andrigid port 26 b returns the dialyzed blood to the patient (venous line)Rigid ports 26 e sends unprocessed blood to the dialyzer and rigid port26 a receives processed blood returning from the dialyzer. Rigid port 26d pulls spent dialysate (ultrafiltration) from the dialyzer and rigidport 26 d delivers fresh dialysate to the dialyzer. Rigid ports 26 dcould alternatively be patient ports for performing PD. Port 26 f is thesaline or priming fluid port. The heparin port is not shown but islocated midway between ports 26 d and 26 e.

FIG. 4 illustrates a vent port 26 g. Vent port 26 g can vent air fromair separation chamber 50 to atmosphere or to drain in differentembodiments. Cassette 10 can include other apparatuses (notillustrated), such as pressure sensing areas, a heater flow path area(discussed below in connection with FIG. 13), and additional pumpingareas, such as heparin and/or saline pumping areas (e.g., via diaphragmor peristaltic pump).

FIGS. 3 and 4 show one embodiment of the air separation chamber or airtrap of the present disclosure, namely, air separation chamber 50 a. Airseparation chamber 50 a shows a portion of cassette 10 for reference,although it should be appreciated that air separation chamber 50 a (andothers discussed below) can be provided as a stand-alone component,e.g., housing 10 is a stand-alone unit. Here, the stand-alone cancommunicate fluidly with the disposable cassette via tubing.

Air separation chamber 50 a includes a first side wall 52, a bottom wall54, a second side wall 56 and a top wall 58. As seen in FIGS. 1 and 2,mid-plane 18 extends along the outside of walls 52 to 58 but not insideair separation 50, such that walls 52 to 58 extend the entire thicknessof cassette 10. Here, both broad surfaces of air separation chamber 50can be made of flexible sheeting 28, both can be made of rigid material,or one be made of rigid material while the other is made of flexiblesheeting 28. For example, a piece of rigid material in the profile shapeof air separation chamber 50 a can be welded or solvent bonded to one orboth sides of walls 52 to 58. Thereafter, the sheeting is welded orsolvent bonded to the edges of the rigid broad side(s) of air separationchamber 50 a to covert the remainder of cassette 10.

Inlet port 26 b and outlet port 26 a can be cassette flow paths as seenin FIGS. 1 and 2 or stand-alone flow passages 62 and 64 as shown inFIGS. 3 and 4. Inlet and outlet pathways 62 and 64 can be cassette flowpaths as seen in FIGS. 1 and 2 or stand-alone flow passages as shown inFIGS. 3 and 4. In FIGS. 3 and 4, inlet pathway 62 and outlet pathway 64communicate with air separation chamber 50 via inlet 66 and outlet 68,respectively, which are formed in first side wall 52 of air separationchamber 50. The inlet and/or outlet pathway communicates alternativelywith air separation chamber 50 via an outlet 68 formed in second sidewall 56 of air separation chamber 50 as illustrated in FIG. 9 a.

The air separation chamber vent valves are not shown in FIG. 3 and FIG.4. An external valve, or external valves, open and close a vent lineconnected to disposable cassette 10, which communicates with vent port26 g and with air separation chamber 50 a via a vent outlet 70 seen inFIG. 3. External dual vent valve chambers, similar to 20 k and 20 l inFIGS. 1 and 2, allow the controller unit of the dialysis instrument toisolate a slug of air in the vent line before vent valve chamber 20 l isopened, allowing the air to escape via vent port 26 g to atmosphere ordrain. In the programmed sequence, with vent valve chamber 20 l closed,vent valve chamber 20 k is opened allowing the vent line to becomepressurized with air. Once the vent line becomes pressurized, valvechamber 20 k is closed and valve chamber 20 l is opened, relieving thepressure in the vent line.

With air separation chamber 50 a, inlet pathway 62 and outlet pathway 64are parallel to each other and are at least substantially perpendicularto the vent line. Side walls 52 and 56 are at least substantiallyorthogonal to walls 54 and 58, forming a square or rectangular airseparation chamber 50 a. FIG. 3 also shows the top 58 being tapered tosmooth flow and prohibit air trapping. Likewise, bottom 54 can betapered especially when the fluid inlet occurs on the bottom of the airseparation chamber and impinges an upper plenum forming wall such asbaffle portion 82 b discussed below.

As seen in FIGS. 3 and 4, air separation chamber 50 a includes a baffle80 a, which as illustrated includes a baffle portion 82 a extendingvertically upward from bottom wall 54 past inlet 62. A second baffleportion 82 b jogs inwardly from baffle portion 82 a, e.g., at anon-horizontal angle, into chamber 50 a forming an inlet plenum. A thirdbaffle portion 82 c jogs upwardly from baffle portion 82 b, e.g.,vertically, extending past outlet 64. Wall 82 d angles inwardly frombaffle portion 82 c, e.g., at a non-vertical angle, into chamber 50 a,forming the bulk of baffle 80 a.

Baffle 80 a forces the flow of dialysis fluid vertically upward frominlet 62 and inlet plenum against the force of gravity g, along firstbaffle portion 82 a of baffle 80 a. Dialysis fluid hits baffle portion82 b and is forced to change direction. Dialysis fluid is then squeezedbetween baffle portion 82 c and an outer surface (e.g., flexiblesheeting) of the air separation chamber before extending verticallyalong primary baffle portion 82 d, flowing over a free edge 82 e ofbaffle portion 82 d and down along baffle portion 82 d into a plenumcreated by the back side of 82 c and exiting air separation chamber 50 athrough exit opening 68 and outlet pathway 64.

The angle of baffle portion 82 d causes the cross-sectional area of thedialysis fluid flow to increase and the fluid velocity to decrease as itrises up the inlet side of the baffle wall. The slowing of the dialysisfluid flow allows buoyancy forces more time to lift air bubbles from thedialysis fluid to an air collection portion of the air trap. As thefluid flow downward towards the outlet, the cross-sectional area of thedialysis fluid flow also increases and the fluid velocity decreases.This further increases the buoyancy force while decreasing the dragforce.

Referring now to FIG. 5, air separation chamber 50 b operable withcassette 10 includes a different baffle or separation wall 80 b. Here,as with chamber 50 a, inlet 66 and outlet 68 are both formed in sidewall 56, with inlet 66 located below outlet 68. Alternatively, one orboth of inlet 66 and outlet 68 is/are formed in side wall 52 (not seenhere). Vent opening 70 is located here in top wall 58 of air separationchamber 50 b. Inlet 66, outlet 68 and vent opening 70 operate withcassette-based or stand-alone pathways as described above. Inlet 66,outlet 68 and vent opening 70 operate with associated valve chambers asdescribed above.

As seen in FIG. 5, air separation chamber 50 b includes a baffle 80 b,which as illustrated includes a baffle portion 82 a extendinghorizontally from side wall 56 to side wall 52. If either surface 72 or74 of air separation chamber 50 b is rigid, baffle portion 82 a can beformed with or adhered to surface 72 and/or 74. If either surface 72 or74 of air separation chamber 50 b is made of flexible sheeting 28, thesheeting can be welded or bonded to baffle portion 82 a. Baffle portion82 a forms an inlet plenum over inlet 66.

A second baffle portion 82 b jogs upwardly from baffle portion 82 a. Athird baffle portion 82 c extends upwardly from baffle portion 82 b,clears outlet 68, and tapers inwardly from face 72, e.g., at an anglefrom vertical, into chamber 50 a, forming the bulk of baffle 80 b. A jog82 d on the outlet side of baffle 80 b forms an outlet plenum for outlet68.

Dialysis fluid hits horizontal baffle portion 82 a of baffle wall 80 band is funneled towards face 72. Baffle portion 82 b forces the flow ofdialysis fluid vertically upward from inlet 62 and inlet plenum 82 aagainst the force of gravity g, along second baffle portion 82 b andsqueezes the dialysis fluid between baffle portion 82 b and face 72(e.g., flexible sheeting) of the air separation chamber. Dialysis fluidthen extends vertically along primary baffle wall 82 c, flows over freeedge 82 e of baffle portion 82 c and exits air separation chamber 50 bthrough exit opening 68.

The taper of baffle portion 82 c causes the cross-sectional area of thedialysis fluid flow to slow as it rises up the inlet side of baffle 80b. The slowing of the dialysis fluid flow allows buoyancy forces moretime to lift air bubbles from the dialysis fluid to an air collectionportion of the air trap.

Air separation chamber 50 b also includes an upper baffle wall 84, whichprevents fluid from exiting vent port 70 when air is vented from airseparation chamber 50 b. The bottom surface of baffle 84 is preferablyangled upward so that air bubbles will tend to flow into the airaccumulation chamber above baffle 84. FIG. 6 illustrates an output of asimulation of air separation chamber 50 b of FIG. 5, showing pathwaystaken by one-hundred micron diameter air bubbles trapped within thedialysis fluid when flowing through air separation chamber 50 b,calculated to have a 0.0005 micro-liter volume, wherein the dialysisfluid flowrate is about 500 ml/min and the pressure drop through the airtrap is about 0.1 psi. Thus, the drag force of the rapidly flowing bloodstream (μblood=3.62 cP and ρblood=1.06 g/cc) will pull 100 microndiameter bubbles will flow through the air trap.

FIG. 7 illustrates an output of a simulation of air separation chamber50 b of FIG. 5, showing pathways taken by two-hundred-fifty microndiameter air bubbles trapped within the dialysis fluid when flowing intoair separation chamber 50 b, calculated to have a 0.008 micro-litervolume, wherein the dialysis fluid flowrate is about 500 ml/min and thepressure drop through the air trap is about 0.1 psi. Most of the 250micron diameter air bubbles are to the top of the air separationchamber; however, some flow through the air trap.

FIG. 8 illustrates an output of a simulation of air separation chamber50 b of FIG. 5, showing pathways taken by three-hundred micron diameterair bubbles trapped within the dialysis fluid when flowing through airseparation chamber 50 b, calculated to have a 0.014 micro-liter volume,wherein the dialysis fluid flowrate is about 500 ml/min and the pressuredrop through the air trap is about 0.1 psi. All of the 300 microndiameter air bubbles float to the top of the air separation chamber.Thus, this air trap design, which is about 5 cm by 5 cm by 1.25 cm insize, can be expected to provide a significant margin between actual andrequired performance since our goal was to not pass air bubbles largerthan 1 micro-liter in volume. The air bubble detector in the venous lineis intended to detect and sum the volume of air bubbles larger than 1micro-liter in volume that pass by it. An alarm will be posted and thetherapy halted if this volume exceeds various thresholds per unit time.Our goal is to almost never encounter an alarm.

FIGS. 9A and 9B illustrate air separation chamber 50 c, which includesalternative apparatus to the previous air separation chambers. Airseparation chamber 50 c includes inlet 66/pathway 62 and outlet68/pathway 64 placed on opposite sides walls 52 and 56 of air separationchamber 50 c. Inlet 66/pathway 62 and outlet 68/pathway 64 are locatedalternatively on the same side wall 52 or 56. Baffle 80 c includes firstand second baffle portions 82 a and 82 b, which are the same or verysimilar to that of air separation chamber 50 b of FIG. 5. Baffle portion82 c is angled rather than tapered, however, providing more fluid volumeper package size than air separation chamber 50 b of FIG. 5. Baffle 80 cincludes an upper horizontal baffle portion 82 d ending at free edge 82e, while forming an exit dialysis fluid plenum with outlet 68.

Baffle 80 c further includes an integrated air vent valve chamber 90,including a valve chamber wall 92, valve port 94 and vent outlet 96 tovent channel 98. Face 74 or at least the portion of face 74 covering airvent valve chamber 90 is formed via flexible sheeting 28. When air ventvalve chamber 90 is closed, air cannot pass through port 94, thoughoutlet 96 to channel 98. When air vent valve chamber 90 is open, air canpass through port 94, though outlet 96 to channel 98. A valve chamberdownstream from air vent valve 90 allows for the sealed release of airdescribed above. Integral air vent valve chamber 90 saves space overallfor cassette 10.

FIGS. 10A and 10B illustrate air separation chamber 50 d, which includesalternative apparatus to the previous air separation chambers. Airseparation chamber includes inlet 66/pathway 62 and outlet 68/pathway 64placed on opposite sides walls 52 and 56 of air separation chamber 50 d.Inlet 66/pathway 62 and outlet 68/pathway 64 are located alternativelyon the same side wall 52 or 56. Here, however, inlet 66/pathway 62 islocated above outlet 68/pathway 64. Baffle 80 d further includes anintegrated air vent valve chamber 90, including a valve chamber wall 92,valve port 94 and vent outlet 96 to vent channel 98.

Baffle 80 d includes first and second baffle portions 82 a and 82 b,which are the same or very similar to that of air separation chambers 50b and 50 c. Baffle portion 82 c is angled more severely than baffleportion 82 c of baffle 80 c. Baffle 80 d includes a second verticalbaffle portion 82 d and a second angled baffle portion 82 e, ending atfree edge 82 f. Second angled portion 82 e slows the velocity ofdialysis fluid rising from inlet 66/pathway 62 and also slows thevelocity of fluid returning along angled portion 82 e towards baffleportion 82 b to outlet 68/pathway 64. First angled portion 82 c createsan inlet plenum around inlet 66/pathway 62.

Baffle 80 e of air separation chamber 50 e of FIGS. 11A and 11B is thesame as baffle 80 d of air separation chamber 50 d of FIGS. 10A and 10B.The primary difference between air separation chamber 50 e and airseparation chamber 50 d is the placement of inlet 66/pathway 62 andoutlet 68/pathway 64, which are both vertically disposed and operablewith bottom wall 54. The inlet plenum also has a second baffle 86, whichprovides a serpentine pathway through the inlet plenum. The serpentinepathway extends the length of the pathway and is intended to distributethe inlet flow as uniformly as possible over the length of the inletplenum before it begin to pass vertically along separation wall 80 e.

Cross-sectional area increases and slows the flow of dialysis fluid onthe inlet and outlet sides of baffle 80 e here via angled baffle portion82 c, while baffle portion 82 e decreases cross-sectional area andspeeds the flow in both cases. Vertical inlet 66/pathway 62 and outlet68/pathway 64 can be switched from the position shown in FIGS. 11A and11B.

Referring now to FIG. 12, a further alternative air separation chamber50 f is illustrated. Here, the air separation chamber operates with aheating chamber 100. Heating chamber 100 includes a heating wall 102,which accepts heat from a heater element (not shown) such as a resistiveor inductive heater element. As illustrated in FIG. 12, heating wall 102has a substantially circular cross-section. Heating wall 102 transmitsheat to fluid flowing within hybrid air separation chamber 50 f/heatingchamber 100, e.g., from inlet 62 to outlet 64. Baffles 104 are providedto increase heating contact time with wall 102 and to increase fluidmixing.

Baffles 104 also aid in allowing air to separate from the dialysis fluidas described herein. The baffles can be staggered and inclined topromote movement of air towards the top of air separation chamber 50f/heating chamber 100, where air outlet 70 is located. A splash wall isprovided to prevent liquid from exiting through air outlet 70.

Referring now to FIG. 13, yet another alternative air separation chamber50 g is illustrated. Here, the air separation chamber includes dual,e.g., concentric, tubes 110 and 112. Tubes 110 and 112 can have variousshapes, for example, circular, rectangular, elliptical, or oval shape.Tubes 110 and 112 can be formed as part of cassette 10, fixed tocassette 10 or connected fluidly as a stand-alone device to cassette 10via tubing connection. Tube 110 includes a dialysis fluid inlet 114 andan air vent outlet 116 as shown. Air vent outlet 116 can operate withmultiple air vent valves as discussed above.

Inner tube 112 extends upwardly into outer tube 110 when air separationchamber 50 g is mounted for operation. Fluid enters air separationchamber 50 g from inlet 114, flows upwardly within outer tube 110, flowsover a free end 118 of tube 112, flows down tube 112 and out dialysisfluid outlet 120. Although not illustrated, tube 110 can have bafflesthat increase the flow path within tube 110. Also not illustrated, tube110 can have a splash plate that prevents fluid from exiting through airvent outlet 116.

Any of the air separation chambers discussed herein can operate with amesh screen, e.g., in the two-hundred-fifty micron range to preventparticulates and clots from being returned to the patient. The mesh canalso act as a nucleus for bubble formation when outgassing occurs. Themesh can be located at the fluid outlet of the air separation chamber orcan extend across the top of the separation wall so that all flow mustpass through it before entering the exit plenum.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present subjectmatter and without diminishing its intended advantages. It is thereforeintended that such changes and modifications be covered by the appendedclaims.

1. A dialysis fluid system comprising: a dialysis instrument including apump actuator and a fluid heater; and a dialysis fluid cassetteincluding a rigid portion and a flexible sheet cooperating to form apumping section for operation with the pump actuator, the dialysis fluidcassette further including a heating section for operation with thefluid heater, the heating section including a dialysis fluid inlet, adialysis fluid outlet, and a dialysis fluid heating area located betweenthe fluid inlet and the fluid outlet, and an air vent opening locatedabove the fluid outlet when the dialysis fluid cassette is loaded intothe dialysis instrument.
 2. The dialysis fluid system of claim 1,wherein the heating section, is structured and arranged to accept heatfrom an inductive heating element.
 3. The dialysis fluid system of claim1, wherein the heating section includes a heat transfer wall in fluidcommunication with the dialysis fluid inlet and the dialysis fluidoutlet.
 4. The dialysis fluid system of claim 3, wherein the heattransfer wall is at least substantially circular in cross-section. 5.The dialysis fluid system of claim 1, wherein the heating sectionincludes a plurality of baffles configured to increase heat transfer. 6.The dialysis fluid system of claim 1, wherein the dialysis instrumentincludes a valve actuator and wherein the rigid portion further definesat least one valve chamber.
 7. The dialysis fluid system of claim 1, theheating section including a plurality of baffles configured and arrangedto promote movement of air towards the air vent opening.
 8. The dialysisfluid system of claim 1, the heating section including a splash walllocated below the air vent opening, the splash wall configured andarranged to prevent fluid from exiting via the air vent opening.
 9. Adialysis fluid system comprising: a dialysis instrument including a pumpactuator and a fluid heater; and a dialysis fluid cassette including arigid portion and a flexible sheet cooperating to form a pumping sectionfor operation with the pump actuator, the dialysis fluid cassettefurther including a heating section for operation with the fluid heater,the heating section including a dialysis fluid inlet, a dialysis fluidoutlet, and a dialysis fluid heating area located between the fluidinlet and the fluid outlet, the heating section further including an airseparation chamber for collecting air separated from the dialysis fluid.10. The dialysis fluid system of claim 9, wherein the air separationchamber is formed as part of the heating section of the dialysis fluidcassette.
 11. The dialysis fluid system of claim 9, wherein the dialysisfluid air separation chamber is in fluid communication with an air ventopening.
 12. The dialysis fluid system of claim 9, wherein the heatingsection, is structured and arranged to accept heat from an inductiveheating element.
 13. The dialysis fluid system of claim 9, wherein theheating section includes a heat transfer wall located in fluidcommunication with the dialysis fluid inlet and the dialysis fluidoutlet, the heat transfer wall configured and arranged to be heated bythe heater and transfer heat to the dialysis fluid.
 14. The dialysisfluid system of claim 13, the heat transfer wall is at leastsubstantially circular in cross-section.
 15. A dialysis fluid heatingmethod comprising: flexing a sheet of a dialysis fluid cassette to pumpa dialysis fluid through a dialysis fluid air separation chamber of thedialysis fluid cassette; using buoyancy forces to remove air from thedialysis fluid pumped through the air separation chamber; and heatingthe dialysis fluid pumped through the air separation chamber.
 16. Thedialysis fluid heating method of claim 15, which includes inductivelyheating the dialysis fluid.
 17. The dialysis fluid heating method ofclaim 15, which includes resistively heating the dialysis fluid.
 18. Thedialysis fluid heating method of claim 15, which further includescausing the dialysis fluid to change direction at least one time in theair separation chamber to help separate air from the dialysis fluid. 19.The dialysis fluid heating method of claim 15, which includes preventingthe dialysis fluid from escaping from the air separation chamber. 20.The dialysis fluid heating method of claim 15, which includestransmitting heat to a wall of the air separation chamber, causing thewall to heat the dialysis fluid pumped through the air separationchamber.
 21. The dialysis fluid heating method of claim 16, whereinpumping the dialysis fluid includes pumping blood or dialysate.
 22. Adialysis fluid system comprising: a dialysis instrument including a pumpactuator and a fluid heater; and a dialysis fluid cassette including arigid portion having a pumping section for operation with the pumpactuator and a heating section for operation with the fluid heater, theheating section including a dialysis fluid inlet, a dialysis fluidoutlet, and a dialysis fluid heating area located between the fluidinlet and the fluid outlet, an air vent opening located above the fluidoutlet when the dialysis fluid cassette is loaded into the dialysisinstrument, and a plurality of baffles configured to increase heattransfer.